This application claims the priority of German patent document 101 47 732, filed 27 Sep. 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method of triggering a vehicle occupant restraining device.
In a method of this generic type disclosed in U.S. Pat. No. 5,999,871, the severity of the crash is determined by means of an acceleration signal which is supplied by an acceleration sensor. If this acceleration signal reaches a defined threshold value, it is deemed to reach the decisive severity of a crash. The restraining device—here, a first stage of an air bag—is triggered immediately. In this triggering algorithm, it is difficult to distinguish between an actual crash, and extreme stress to the vehicle, which occurs for example, during a fast drive along a gravel and pothole covered route. Accelerations occur in the latter case which are comparable to those of an actual crash. In order not to trigger the restraining device during such a drive, the decisive threshold value is increased in the factory. As a result, in the event of a crash, the restraining device may not be triggered or at least may not be triggered in time.
An additional fact is the lack of conformity of the response behavior of the sensor in the case of different vehicles of the same manufacturer and of the same type. It was found that the stability of macroscopically identical vehicles may differ. Since the method of operation of an acceleration sensor depends on its stability, the triggering of the restraining device differs while it is naturally assumed that the crash is identical in the case of vehicles of the same construction.
It is an object of the invention to provide a method of the initially mentioned type which achieves a constant and reproducible triggering point in time for the restraining device.
This and other objects and advantages are achieved by the method according to the invention wherein a timer is started when a first low crash severity occurs. In this case, it will not be necessary to differentiate between the above-mentioned very stressful drive and a crash, so that it is permissible for the timer to be triggered during such a drive. The crash event will be clearly recognized only by an additional triggering condition, in the form of the occurrence of a higher crash severity.
The triggering time for the restraining device is again determined by the timer. The restraining device will be triggered at the end of the running time of the timer if the higher severity of the crash has occurred during this running time. As an alternative, if the higher crash severity does not occur before the end of the running time, triggering takes place thereafter, as soon as a higher crash severity does occur, provided only that the timer has not yet been reset. Such resetting takes place as soon as the analyzing unit has clearly recognized that no crash is occurring, for example, by means of a “0” value of the acceleration sensor signal. As an alternative, deactivation can take place based on an independent criterion, such as the resetting of the alarm by means of a Saving sensor.
With such an arrangement, it is possible to immediately trigger one or more restraining devices during the running time of the timer if a still higher crash severity is reached during this time. While the one such restraining device may be, for example an active knee guard, another, which will be triggered immediately when a crash of a particularly high severity occurs, may be, for example an air bag.
According to one embodiment of the invention, triggering of the restraining device takes place under the conditions                “counter reading=0” and        “occurrence of a higher crash severity”.        
In this case, it is not important which of the two conditions occurs first. The ignition circuit will only be triggered when both conditions have been met. If no ignition takes place, the timer will be deactivated again.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.